Fatty food increases risk of depression: Study

Eating fatty junk food increases the risk of depression, results of a large new study suggest.

Researchers who followed more than 12,000 Spanish university graduates for six years found the more trans fats consumed, the greater the risk of being diagnosed with depression.

By contrast, olive oil was associated with a lower risk of the debilitating mood disorder.

The study — modelled after the massive U.S. Nurses Health Study — involved a Mediterranean population whose average daily intake of the artery-clogging fats was actually fairly low. Trans fats made up only 0.4 per cent of the total energy ingested by the volunteers.

As well, the two main sources of trans fats were natural foods — cheese and whole-fat milk.

“So, the repercussion of these results might be really important in other settings such as the American population,” the authors write. That’s because Americans — and Canadians — eat far more trans fats than people in Spain, and they get them from more highly-processed “artificial” foods.

Trans fats are created by pumping hydrogen into liquid oil at an elevated temperature, raising the levels of low-density lipoprotein or “bad” cholesterol in the body and increasing the risk of cholesterol buildup in the arteries and heart attack.

Canadians consume, on average, an estimated 3.4 grams of trans fat per day, or about 1.4 per cent of food energy, according to a 2009 report by Health Canada scientists. And while the amount of trans fats in Canadian foods is falling, they’re nowhere near as low as foods in Denmark, where a regulatory ban exists.

The link between foods and mental illness isn’t new. In June, Montreal researchers reported that omega-3 supplements can help ease symptoms of depression.

But people who eat more trans fats — “junk food” kinds of food — are also more likely to be smokers, to drink alcohol and to engage in other behaviours that might increase their risk of depression.

“We need to make sure that we just don’t say it’s the diet alone — there are other factors associated with the diet that may be driving the relationship,” said Dr. Valerie Taylor, mental health lead at the Canadian Obesity Network and assistant professor at St. Joseph’s Healthcare in Hamilton, Ont.

“Which comes first? Is it the chicken or the eggs? People who become depressed often don’t care about their health as much, so they’re going to be less likely to eat healthy,” she adds.

That being said, Taylor said more evidence is suggesting that processed foods are impacting mental health and cardiovascular health in ways we don’t fully understand.

Cardiovascular disease and mental illness are both associated with inflammation, Taylor said. Inflammation occurs when people gain weight.

“It may be that because of the trans fats, the weight is going up, the body is producing inflammatory markers and that’s making the depression worse,” she said. “These relationships make complete sense.”

She stressed that people shouldn’t stop taking their anti-depressants and start taking omega-3 supplements or change their diet “and assume that that’s going to be enough.”

But people who have experienced depression in the past often ask, ‘what can I do to help prevent this from happening again?’

“Avoiding foods with trans fats certainly can’t harm you and we know from a cardiovascular perspective it’s going to make a difference,” Taylor said. “Studies like this show it may very well make a difference from a mental-illness point of view as well.

“Does it explain all mental illness? Absolutely not. Should people have a look at this and, if they’re worried and want to do things that are preventive, start to change their diet? Absolutely.”

About one in eight adults in Canada will experience depression at some point in their lives.

Worldwide, depression affects about 151 million people, but wide variations exist between countries. That suggests differences in risk factors — including food habits — might play a role.

The study, published in the journal PLoS One, involved 12,059 initially healthy university graduates, average age 37, who were free of depression at the start of the study. Researchers took a comprehensive assessment of diet — including fat intake — and lifestyle. They excluded anyone who reported a previous diagnosis of depression or were taking anti-depressants.

At the end of the study, 657 new cases of depression had been detected.

The researchers looked at how different types of fats related to the risk of becoming depressed during followup.

They found a “dose response” effect with trans fats — volunteers with the highest intake of trans fats were 42 per cent more likely to report a new diagnosis of depression. The finding held after researchers took sex, age, smoking, physical activity, body mass index and other risk factors into account.

Olive oil and polyunsaturated fats (which are found in fish and in vegetable oils) appeared to protect against depression. The magnitude of the effect wasn’t as strong as it was for trans fat, “but it was significant,” said co-author Dr. Miguel Angel Martinez-Gonzalez, professor of preventive medicine at Spain’s University of Navarra.

The paper doesn’t prove cause and effect, just an association, however, “Even with this low amount of trans fat we are finding a relationship” with depression, Martinez-Gonzalez said — “a relationship that is likely to be stronger in those countries with a high concentration of trans fatty acids.”

The team excluded early cases of depression that were detected in the first two years of followup.

“When you exclude the early cases you can be pretty sure the cases occurring after four, five years were not present at the beginning,” Martinez-Gonzalez said, suggesting that, “First it’s the trans fat, then it’s the depression.”

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